My hopes for SMN, to make it more engaging and less braindead:
1) Eiliminate the mandatory Summon Bahamut/Phoenix condition to access the 3 lego summons and make them ready to use;
2) Instead of spend gems to summon, make so you fill a "gem gauge" when you summon;
3) Let me repeat lego summons if I see fit to do so;
4) Return Outburst as basic AoE spell and move Tri-disaster back to an oGCD that now gets ready whenever the Gem gauge is filled and spend the gauge gems when used, enabling the legos to be summoned again afterwards;
5) Put Energy Drain/Syphoon at 30 secs CD again and replace Fester with an oGCD Ruin IV;
6) Delete Carbuncle (as a dummy pet on the field) and add it as a separate support summon that apply a shield to party and go away after using its skill;
7) Being the summon with your hardcasts, make so Ifrit is the one providing the most damage of all summons and make his abilities single target.
8) Make Garuda's abilities all AoE oriented turning it into a summon specialized in AoE damage again (in dungeons, add phases, etc)
9) Keep Titan the instacast single target summon to go but reduce its AoE effectiveness;
10) Give back to Phoenix its two spell combo, instead of mashing the same button for six times;
11) Make Bahamut/Phoenix uses their attacks only when we use their spells like it was in ShB. There'll probably be no issues with ghosting their first attack now that their Summon skill is GCD;
12) Remove the limit of Gemshine spell casts for your current elemental attunement.
So basically: split Demis from I/T/G and make legos rotation its own system, let us repeat the summons that fill the gem gauge instead of forcing us to use all three needlessly and make them more specialized again (Ifrit the stronger one with single target hardcast spells and abilities, Titan with single target instacast spells and abilites, and Garuda with AoE hard and insta cast spells and abilities)